For many years, transfer printing processes have been employed in the textile industry for printing designs and colours onto the surface of fabrics, particularly synthetics such as double-knit polyester. Transfer printing techniques generally involve the transfer of a sublimation dye composition from an ink-carrying substrate, such as a web of paper, a metallic foil, or a plastic film, onto the fabric surface to be printed. The sublimation dyestuffs may be coated onto a heat resistant carrier such as a paper substrate by means of conventional printing techniques, for instance, gravure printing. Thereafter, the coated surface of the substrate is placed in intimate frictional contact with the fabric surface to be printed and both the fabric and substrate are subjected to heat and pressure, which results in the dye subliming from the surface of the substrate and depositing on the fabric to form a permanent design thereon. Typically, sublimation temperatures for known sublimation dye compositions are in the approximate range of a 125.degree. to 235.degree. C.
Prior to the advent of transfer printing in the textile industry, the duplex printing of fabrics was accomplished using conventional printing techniques. For instance, U.S. Pat. No. 3,398,680 issued to one Moskowitz on Aug. 27, 1968, discloses a duplex fabric printing machine which employs traditional rotary screen printing. Moskowitz teaches the use of opposing screen rollers containing printing fluids therein. The screen rollers according to Moskowitz are held in contact against the fabric web to be printed, each colour of a multi-colour pattern or each design element thereof being applied serially. In contradistinction, transfer printing technology allows for more convenient and simplified operation, as multi-coloured printing inks or complex patterns may be disposed on the same substrate so that a single pass may suffice for achieving the desire printing effect on a fabric surface.
As for the more recent transfer printing techniques, the prior art machines and methods for effecting double-sided printing onto synthetic materials are generally inefficient in operation. For instance, U.S. Pat. No. 3,874,846 issued on Apr. 1, 1975 to one Ashe, discloses a method for transfer printing on opposite faces of a web of grey goods double-knit from a synthetic material. The transfer printing technique according to Ashe employs a pair of heated rotating cylinders which are disposed in tandem to thereby effect the printing of each fabric face sequentially. Moreover, each heated cylinder disclosed in the Ashe reference is provided with an endless belt for urging the fabric web and transfer paper thereagainst.
It is accordingly an object of the present invention to provide a method and an apparatus for transfer printing onto both sides of a web of fabric simultaneously, thereby overcoming the problems occasioned in the prior art devices and methods in which printing is performed sequentially on each face of the fabric. As such, it is an object of the present invention to eliminate design duplication and the additional capital and operating costs associated, for instance, with the provision of two serial heating stations as exemplified by known duplex transfer printing techniques.
It is another object of the present invention to provide a method and an apparatus for transfer printing wherein the fabric web to be printed is conveyed by the ink-carrying substrates which are disposed in intimate frictional contact therewith, to thereby eliminate the need for endless belts or other means in order to convey and support the fabric and printing substrates as found in the prior art.
It is yet another object of the instant invention to provide a method and an apparatus for simultaneous duplex transfer printing which result in lower costs of installation and operation, and provide for reliable and simplified printing of fabric webs of indefinite length, when compared to known techniques of transfer printing.